The present invention relates to ninety degree couplers suited for use in integrated circuits operating between 100 mHz to GHz ranges.
Ninety degree couplers are used in many radio frequency integrated circuit (RFIC) applications. Couplers split or combine two orthogonal signals. This kind of coupler is used in balanced amplifiers, mixers, particularly Gilbert cell mixers, balanced attenuators, signal splitters and signal combiners. Particularly popular use for ninety degree couplers is in cell phones. Cell phone signals are multiplexed into In-phase, I and Quadrature panels. Ninety degree couplers are used to bind the signals for transmission and separate them for reception. Currently, the predominant form on ninety degree coupler for RFIC applications is an RC network. Couplers have been provided in MMIC technology and GaAs processing. However, greater simplicity can yet be achieved. It is desirable to minimize the number of components in a ninety degree coupler. This allows a smaller IC area. Reducing area permits reduce costs and insensitivity to spurious signals.
In accordance with the present invention, a ninety degree coupler is provided for a frequency range of 100 mHz to 2500 mHz and beyond to accommodate new frequency bands and including a minimum number of components.
Briefly stated, in accordance with the present invention, there is provided a four port device which receives an input at port 1. The signal is split between a transformer coil and another reactor. In one form, the signal entering port 1 splits between the transformer and a capacitor. Part of the signal is coupled to port 2 through the transformer by mutual inductance. Another part of the signal couples through cross-connected capacitors. Phase shift created by the inductors and capacitors result in signals adding at ports 2 and 3 and signal cancellation at point 4. Phase of the signal shift from port 1 to port 2 is 45 degrees and from port 3 is xe2x88x9245 degrees. Thus the phase shift between the signal and ports 2 and 3 is 90 degrees and remains 90 degrees over a wide frequency band. In another embodiment, a signal passes around from port 1 to port 2 to port 3 to port 4 with a ninety degree phase delay at each port. The power from port 1 will be equally split between port 2 and port 3 and the phase of the signal will be 90 degrees and 180 degrees respectively, providing a 90 degree phase shift across ports 2 and 3.